This invention relates to endless conveyor systems for use in industrial manufacturing processes, and more particularly to an endless conveyor for feeding raw wood material into a multiple cut saw machine.
Multiple cut saw machines have been developed for making two or more angular cuts at either end of a wood member by the use of two or more pairs of laterally-spaced circular saws. These saws are positionable adjacent to an endless conveyor system which is adapted for receiving raw lumber at one end and either fixedly holding or loosely pushing the lumber while conveying it along a cutting path where it subsequently is cut by the saws.
Early saw machines utilized conveyors with a series of lugs or backrests which attempted to push the lumber, standing on edge, along the conveyor and through the saws. If the lumber was twisted or warped, or if its edgewise height was greater than that of the lug or backrest it was susceptible to falling forward or rearward over the backrest, thereby placing the lumber in an improper position for cutting and creating a possible hazard for saw operators.
A variety of attempts have been made to provide greater stability as the lumber was moving along the conveyor and through the saws. Some saws use slide rails or powered conveyor chains positioned above and contacting the lumber and running parallel to the main conveyors. These are only moderately successful and create at least two potential hazards, one being the saw operator must often physically stabilize the lumber while it engages the upper guide or conveyor, and the other being the interfacing of saw blades with the overhead guides or conveyors as saws are rotated into position for certain angular cuts.
One attempted improvement over the conveyor systems described above may be found in U.S. Pat. No. 3,388,727, issued June 18, 1968, which discloses a machine of the general type referred to herein, wherein the conveyor comprises an endless chain assembly having outward projections or dogs spaced at predetermined intervals along the chain links. These dogs are arranged in pairs, the trailing dog having a flat rectangular surface for seating against the lumber, and the leading dog having a sharp rearward spike for embedding into the lumber to firmly hold it while it travels along the conveyor chain. A further disclosure of this invention may be found in U.S. Pat. No. 3,416,643, issued Dec. 17, 1968. The disclosures of these patents suffer from several disadvantages, which disadvantages are also common to other known devices in the prior art. Since the conveyor dogs are attached directly to the conveyor chain, their flexibility of use and position is directly related to the chain itself. For example, the dogs are intended to be spaced apart by a fixed distance along the conveyor chain such that a "standard" dimension piece of lumber will be clamped between them with a predetermined force. To the extent that "standard" lumber varies from the dimensions commonly though to be standard, the clamping force provided by the dogs may be more or less than that required for adequately supporting the lumber. If a given piece of lumber deviates from standard dimensions by being wider than normal, it may place an undue strain on the clamping dogs, which strain is transmitted directly to the chain as a stretching force. Repeated instances of handling nonstandard sized lumber may prematurely weaken or damage the chain, and further may move the dogs to spaced apart positions which cause them to inadequately clamp normal or undersized pieces of lumber. Further, the lumber that is clamped between the dogs may have an imperfect vertical position resolution. Since the clamping action of the dogs is accomplished while they are traveling around a circular sprocket, there may be a tendency for the lumber to shift vertically before the front dog is firmly embedded in the lumber. Indeed, the very penetration of the front dog into the lumber may have a tendency to slightly raise the lumber. Once clamped, the lumber will remain in its clamped position regardless of whether it is precisely aligned as is required for the sawing operations. Because of the various problems associated with the previously described clamping conveyor system it has met with little commercial success, and the overhead guide rails and powered conveyors remain the most frequently used state of the art.
There is therefore a need for a lumber clamping mechanism which may be suitable for accepting both undersized and oversized lumber, without causing undue strain to the conveyor chain, and which will reliably and consistently provide a constant vertical and longitudinal reference for the lumber position during the cutting operations.